1. Field of the Invention
This invention relates to an automatic molten substance bagging method and system for automatically filling a bag with a fixed amount of molten substance such as asphalt latex.
2. Description of the Prior Art
An automatic molten substance bagging system of the type mentioned is disclosed in U.S. Pat. No. 4,724,656 granted to the applicant of the present patent application. In the automatic molten substance bagging system, a paper bag is first supplied in a closed condition into a carrying can and transported to an inflator of the air jet type at which air is jetted into the paper bag to compulsorily inflate the paper bag, and then the paper bag is transported to a position below an injector at which the paper bag is attracted on the opposite faces thereof by a set of vacuum attracting pads to open a mouth portion of the paper bag. Then, while the paper bag is kept in the attracted condition, the paper bag is lifted at a stroke to a predetermined vertical position by the vacuum attracting pads until a nozzle of the injector is inserted into the open mouth portion of the paper bag while also the carrying can is lifted at a stroke to a predetermined vertical position. Then, the vacuum attracting pads on the opposite sides of the paper bag are advanced to close the mouth portion of the paper bag, and while the paper bag is maintained in such condition, molten substance is filled into the paper bag from the injector. After the paper bag is filled with a predetermined amount of molten substance, the paper bag is released from attraction by the vacuum attracting pads on the opposite sides, and then the vacuum attracting pads are retracted from the paper bag, whereafter the carrying can is lowered to the original vertical position at which it is to be transported by a conveyor system.
In this manner, in the automatic bagging system, when molten substance is to be filled into a paper bag, the inflator of the air jet type is employed to compulsorily inflate the papaer bag prior to a molten substance filling operation into the paper bag in order to subsequently allow molten substance to extend fully to any corner at the bottom of a paper bag.
Further in the automatic molten substance bagging system, a fixed volume member for determining an amount of molten substance to be filled into a paper bag is disposed such that an axis thereof extends in a horizontal direction, and a piston is fitted for sliding back and forth movement in the fixed volume member and connected to a piston rod of a hydraulic cylinder. The piston of the fixed volume member is thus moved band and forth by the hydraulic cylinder to introduce, on one side of the piston, molten substance into the fixed volume member while it extrudes, on the other side thereof, molten substance from within the fixed volume member.
Accordingly, introduction and extrusion of molten substance are performed alternately on the opposite sides of the piston. In order to achieve such control of flow of molten substance, at least four solenoid valves and a complicated controlling circuit for controlling the solenoid valves are required. Besides, high driving force is required to operate the piston of the fixed volume member to extrude molten substance from the fixed volume member.
Further in the automatic bagging system, molten substance which remains sticking to a valve piston and a lower end of the injector, which is provided to inject molten substance from the fixed volume member into a paper bag, after a nozzle of the injector is closed by the valve piston is blown off by air which is jetted only from a single jetting hole formed at the center of the valve piston. Accordingly, such remaining molten substance cannot be blown off clean. Besides, the closing property of the nozzle by the valve piston is not satisfactorily high.